1. Technical Field
The present invention relates to a plate-fin-type heat exchanger wherein a high temperature fluid or a low temperature fluid flows continuously therethrough, while the other flows intermittently therethrough, and relates to a plate-fin-type heat exchanger wherein thermal fatigue produced particularly in a separating plate partitioning between the passages through which the high temperature fluid flows and the passages through which the low temperature fluid flows is alleviated.
2. Background Art
The plate-fin-type heat exchanger has a large area of heat transfer per unit area and a high coefficient of heat transfer, and therefore has an advantage in that it is compact and easily made in comparison with other types, particularly tube type heat exchangers.
Also, the plate-fin-type heat exchanger has a wide range of selection of design such that the fin pitch, the fin height and the fin shape suitable for the nature and the purpose of the fluid flowing through each passage can be properly selected, and further the number of laminations of fins can be selected arbitrarily, and thereby an efficient design can be made, so that it has been used for a variety of applications.
On the other hand, where such a plate-fin-type heat exchanger is applied to the case where one of a higher temperature fluid and a low temperature fluid performs continuous operation and the other operates intermittently, the temperature of the separating plate which is a partition plate between the fluid passages is largely varied repeatedly, and therefore thermal fatigue is produced, and a long-time use thereof might result in damage.
For the plate-fin-type heat exchanger having the above-mentioned configuration, the temperature of the separating plate between the adjacent passages during operation is given by the following equation. ##EQU1## where, Q: Quantity of heat exchange (Kcal/hr)
hA.sub.H : Coefficient of heat transfer x area of heat transfer (Kcal/h.degree.C.) of high temperature side PA0 hA.sub.L : Coefficient of heat transfer x area of heat transfer (Kcal/h.degree.C.) of low temperature side. PA0 T.sub.H : Temperature of fluid of high temperature side, .degree.C. PA0 T.sub.L : Temperature of fluid of low temperature side, .degree.C. PA0 T.sub.W : Temperature PA0 E: Young's modulus PA0 a: Coefficient of thermal expansion of separating plate,/.degree.C. PA0 .DELTA.TW: (T.sub.W1 -T.sub.W2) PA0 (1) the fin having a high coefficient of heat transfer and a large area of heat transfer is used for the passage wherethrough the heat medium passes continuously during operation, and the fin having a low coefficient of heat transfer and a small area of heat transfer is used for the passage wherethrough the heat medium passes intermittently in a certain time cycle during operation, and the ratio of hAs (coefficient of heat transfer x area of heat transfer) is increased, PA0 (2) the passage continuously passing the heat medium is disposed outside the passage of intermittent side, and PA0 (3) the number of the dummy passages of the outermost side of the heat exchanger core are set to two or more. Or, further, PA0 (4) it is desirable to use the corrugated fin of the lower half of the inlet side of the heat exchanging part in the passage of intermittent part having a coefficient of heat transfer and an area of heat transfer equivalent to those of the corrugated fin of the fluid distributing part.
Here, consideration is made on the temperature of the separating plate in intermittent operation.
When the high temperature side is in normal operation, and the low temperature side is in the stopped state, EQU T.sub.W =T.sub.H.
When the high temperature side is in normal operation, and the low temperature side starts to operate, the temperature T.sub.W is reduced, being balanced at a certain temperature.
Taking the temperature of the separating plate when the low temperature side is inactive as T.sub.W1 (=T.sub.H), and the temperature of the plate balanced after a lapse of some time from start of operation of the low temperature side as T.sub.W2, the temperature of the separating plate varies repeatedly between T.sub.W1 (=T.sub.H) and T.sub.W2. No problem exists if this variation in temperature takes place slowly and uniformly, but actually, this variation occurs in a nonuniform fashion, causing generation of thermal stress.
Next, taking the amount of change in the temperature as (T.sub.W1 -T.sub.W2)=.DELTA.T.sub.W, thermal stress is expressed by the following general equation. EQU .sigma.=Exax.DELTA.T.sub.W
As shown by the above equation, as the amount .DELTA.T becomes smaller, the thermal stress becomes smaller and the life or durability is increased.
However, for the plate-fin-type heat exchanger wherein either of the high temperature fluid and the low temperature fluid passes through intermittently, no heat exchanger has been proposed which has a configuration that the variation in the temperature of the separating plate between the passages is positively minimized, and conventionally materials being resistant to thermal stress have been selected.
The present invention proposes to provide a plate-fin-type heat exchanger wherein the thermal fatigue is alleviated which is produced in the separating plate partitioning between the high temperature passage and the low temperature passage of the plate-fin-type heat exchanger wherein one of the high temperature fluid and the low temperature fluid is operated continuously, while the other repeats intermittent operation, and thereby the life of the heat exchanger is extended.